As a typical example of a symptom accompanied by a pain in a knee joint, knee osteoarthritis is known. Knee osteoarthritis is a case in which a function of a knee joint is impaired by muscle weakness, aging, obesity, and the like, causing wear of knee cartilage, loose engagement of meniscus, deformity, rupture, excessive congestion of synovial fluid due to inflammation, and causes a pain when walking.
An advancement of the knee osteoarthritis may cause a varus deformity due to joint destruction, resulting in bowleg which is commonly called O-leg.
Bowleg is believed to be a cause of the knee osteoarthritis along with knock-knee, which is commonly called X-leg, intimately related to the knee osteoarthritis.
In the case of bowleg, a cartilage inside the knee joint tends to be damaged, and in the case of knock-knee, an outer cartilage tends to be damaged. As the state of the knee osteoarthritis advances accompanied by bowleg or knock-knee, leg curvature becomes severer to make an inclination of the crus still steeper, further wearing the joint cartilage. When bones rub each other directly due to the wear of the cartilage, a strong pain is felt disabling a walk.
To treat the knee osteoarthritis, an operative treatment of sectioning a knee joint and implanting a metallic artificial joint, and a conservative treatment of continuing a rehabilitation using a gait training equipment to recall a memory of correct walking behavior, are known.
With the operative treatment, though the pain of walking is eliminated, there is a drawback that the patient can sit only on a chair due to a narrow rotation angle of the artificial joint and that the patient cannot stand up if both legs have the artificial joint. Another drawback is that the useful life is approximately 10 years because aging may weaken the bone and lose strength balance with metal and therefore a further surgery will be required after the useful life. Furthermore, the operative treatment is expensive.
On the other hand, the conservative treatment is a long-term treatment of relieving the pain while walking using a knee brace and enhancing muscles by regularly walking every day, which requires physical strength and patience of the patient, but does not present the drawbacks unique to the operative treatment.
Accordingly, various knee braces for the conservative treatment have been conceived (see, for example, Patent Document 1).
However, because the knee brace according to Patent Document 1 uses a rack and a gear in joint members on the outer leg side and the inner leg side, the total weight of the knee brace is heavy. Furthermore, a gear sound occurs when walking with the knee brace mounted, imparting discomfort to the patient wearing it.
Moreover, because the joint members on the outer leg side and the inner leg side both use the rack and the gear, not only the correction effect is exerted over an angle range that does not need to be corrected but also the correction is made in an opposite direction within 90-degree flexion, which prevents a smooth movement of the knee.
Now, a relation between the movement of the knee joint in a knee osteoarthritis patient with bowleg or knock-knee and the angle range that needs to be corrected is shown in FIG. 20.
FIG. 20(C) depicts a 90-degree flexed state when sitting on a chair, and FIG. 20(D) depicts a fully flexed state when sitting on heels. Generally the angle between the femur and the crus is about 18 degrees when sitting on heels as depicted in FIG. 20(D), where the knees flex 162 degrees assuming 0 degree in an extended state. In a state of flexing more than 90 degrees, no force is applied to the knee joint and therefore no correction is required.
In the fully extended state when standing as depicted in FIG. 20(B), the angle of the knee is substantially 0 degree, where a force is applied to the knee joint and a correction is required.
In a walking state of a healthy person as depicted in FIG. 20(A), there is a repetition of about 6-degree flexed state of the front stepping foot and up to about 45-degree flexed state of the rear kicking foot, where the highest force is applied to the knee joint in the knee angle range of 0-45 degrees and a correction is required in this range.
As shown in FIG. 20, assuming the fully extended state of the knee as substantially 0 degree in the angle range of the knee osteoarthritis patient with bowleg or knock-knee, the flexing angle of the knee is between 0 and 45 degrees.
The knee brace according to Patent Document 1 uses the rack and the gear in the joint members on the outer leg side and the inner leg side, and therefore the correction effect on the knee joint is constant and linear. The correction effect is exerted over the entire angular range that can be achieved by the knee joint flexing, which in turn prevents a smooth movement of the knee at the flexing angle over 90 degrees causing such troubles as difficulty of sitting on a chair and disability of sitting on heels.
Patent Document 1: JP 2010-69059 A (claims 2, 3; paragraphs 0023-0026, 0034-0037; FIGS. 1, 10)